The present invention relates to mechanical fasteners and, more particularly, to a corrosion resistant fastening system for use with a metallic target in a corrosive, aqueous environment.
The use of fasteners emplaced in a target by means of a powder actuated tool is well known in the art. Extensive commercial use testifies to the versatility and economy of the system. Indeed, the system permits fastenings to be made under conditions which would otherwise render such work very laborious, very costly, or impossible. For example, systems are commercially available which may be used by divers, working at depths of over 200 feet, to fasten objects to submarine steel or concrete structures.
Steel is the basic construction material in marine environments, generally in a conventional low carbon, non-alloyed form. Such steel has no resistance of itself to the previously mentioned corrosive environments. Commonly, therefore, protection against corrosion is sought by painting, coating, sheathing, or cathodically protecting with impressed electric current or sacrificial anodes made of zinc or aluminum, or by a combination of these means. While these measures, to a greater or lesser extent, protect the gross steel structure, they can be ineffective for the relatively small fastener which is driven into the structure. Such fasteners are frequently corroded to the point of uselessness within a year of installation; while, in order to be considered viable, a fastener must retain its integrity for a substantial period, generally about 10 years.